This invention relates generally to steel converters and exhaust-gas treatment systems thereof and more particularly to a method of operating such an exhaust-gas treatment system of a sealed-type converter for operating in a fully sealed state relative to the outside air or a state close thereto in the case wherein, during the blowing process step of the converter, an abnormal situation has arisen and the blowing process has been interrupted.
By the practice of the method of this invention, carbon monoxide, CO, gas of high purity can be efficiently recovered without any danger of explosion or damage to the parts of the exhaust-gas treatment system.
As is well known, the operation of a converter, in general, comprises the three process steps of charging, blowing, and pouring. In the blowing step, as will be described more fully hereinafter, the upstream end of the exhaust-gas treatment system is joined to the mouth of the converter by a hood and its skirt, which closes the gap therebetween. Then pure oxygen is blown through an oxygen lance into the converter and caused to react with the carbon in the molten metal therewith, thereby to accomplish refining.
Thus, a large quantity of CO gas is generated. This CO gas is drawn by an induced-draft fan into the hood and then through a cooler to be cooled, after which dust is removed from the gas, which is stored as a commercially valuable gas in a gas holder.
If this CO gas should leak out into the outside atmosphere, it would be extremely dangerous not only because it can cause carbon monoxide poisoning but also because it readily reacts with the outside air to cause a rapid combustion, and, if it is formed in the low-temperature region of CO gas, the combustion will become instantaneous, that is, an explosion will occur.
For this reason, in order to avoid leakage of CO gas to the outside, it is a common practice in converter operation to maintain the interior pressure within the converter at a negative (gauge) pressure by adjusting a damper for controlling the pressure within the converter. This damper is installed in the exhaust-gas treatment system, for example, between two dust removers. However, this measure causes outside air to be sucked into the hood through the gap between the converter mouth and the skirt, whereby the CO gas concentration is undesirably lowered. That is, the CO gas concentration is sacrificed for the sake of safety.
This infiltration of outside air into the hood in a conventional exhaust-gas treatment system is unavoidable in spite of the lowering of the skirt in the blowing step to close the gap between the converter mouth and the skirt. The reason for this is that, in actual practice, slag tends to accumulate on the rim of the converter mouth, which therefore does not always have a level smooth surface. Consequently, it becomes impossible to obtain an intimate leakproof state of sealing between the skirt and the converter mouth. This common type of converter exhaust-gas treatment system, which is herein referred to as the "semi-open type", is accompanied by the above described problem of lowering of the CO gas concentration.
However, because of a recent rise in the price of CO gas as a commercially valuable gas, there has arisen a need to recover CO gas of high purity as a by-product. In order to meet this need, exhaust-gas treatment systems of recent design have hoods and skirts which are so constructed as to afford a completely leakproof sealed state, or a state very close thereto, between the skirt and the converter mouth during the blowing process step. A system of this character in its operational state relative to the converter is herein referred to that of the "sealed type".
A sealed type converter and its exhaust-gas treatment system, however, is accompanied by the serious problem of explosion, even when it is provided with a special emergency air suction device, when it is operated according to a prior method, as will be described more fully hereinafter.